Hot water apparatus

ABSTRACT

A hot water apparatus includes a burner, a sensible heat recovery heat exchanger, and an ignition plug. The sensible heat recovery heat exchanger includes a case. The ignition plug includes an insulator portion and two electrodes. The insulator portion includes a base end portion and a tip end portion. The tip end portion includes a tip end surface and a groove portion. The tip end surface is arranged opposite to the base end portion. The groove portion is recessed from the tip end surface toward the base end portion. The groove portion is arranged between the two electrodes and provided across top and bottom ends of the tip end portion. The groove portion has a lateral width decreasing from the top end toward the bottom end of the tip end portion.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a hot water apparatus and particularly to a hot water apparatus including a burner and a heat exchanger.

Description of the Background Art

A hot water apparatus including an ignition plug having a plurality of electrodes is disclosed, for example, in Japanese Patent Laying-Open No. 7-190359. In the ignition plug of the hot water apparatus, the plurality of electrodes are held in a base portion (an insulator portion) at a distance from one another. The insulator portion is arranged in a side plate (a wall surface) of a case of a gas burner apparatus.

In the ignition plug described in the publication, condensate generated on the wall surface of the case drops and adheres to the insulator portion. The condensate renders the two electrodes conducting to each other and insulation failure between the two electrodes is disadvantageously caused.

SUMMARY OF THE INVENTION

The present invention was made in view of the problem above, and an object thereof is to provide a hot water apparatus which can suppress occurrence of insulation failure between two electrodes.

A hot water apparatus according to the present invention includes a burner, a heat exchanger, and an ignition plug. The burner generates a combustion gas for heating. The heat exchanger is provided below the burner and heats water and/or hot water with the combustion gas. The ignition plug ignites the burner. The heat exchanger includes a case. The case has a wall surface serving as a partition between the inside and the outside. The ignition plug includes an insulator portion and two electrodes. The insulator portion is attached to the wall surface of the case. The two electrodes extend from the inside to the outside of the case through the respective insulator portions and are arranged at a distance from each other in a lateral direction. The insulator portion includes a base end portion and a tip end portion. The base end portion is attached to the wall surface of the case. The tip end portion protrudes from the base end portion toward a side opposite to the wall surface. The tip end portion has a tip end surface and a groove portion. The tip end surface is arranged opposite to the base end portion. The groove portion is recessed from the tip end surface toward the base end portion. The groove portion is arranged between the two electrodes and provided across top and bottom ends of the tip end portion. The groove portion has a lateral width decreasing from the top end toward the bottom end of the tip end portion.

According to the hot water apparatus in the present invention, the groove portion is recessed from the tip end surface toward the base end portion, arranged between the two electrodes, and provided across the top and bottom ends of the tip end portion. The groove portion has a lateral width decreasing from the top end toward the bottom end of the tip end portion. Condensate which is generated on the wall surface and drops and adheres to the insulator portion is thus more likely to flow through the groove portion. Therefore, connection between the two electrodes by condensate gathered at the top end of the tip end portion and resulting conduction between the two electrodes can be suppressed. Therefore, occurrence of insulation failure between the two electrodes can be suppressed.

In the hot water apparatus, the groove portion has a width increasing from the base end portion toward the tip end surface. Since the condensate is less likely to be gathered at the top end of the tip end portion from the base end portion toward the tip end surface, connection between the two electrodes by the condensate gathered at the top end of the tip end portion and resulting conduction between the two electrodes can further be suppressed.

In the hot water apparatus, the tip end portion includes a first end portion arranged on a first side of the groove portion and a second end portion arranged on a second side of the groove portion. The first end portion has a down grade decreasing in height on a side away from the second end portion. The second end portion has a down grade decreasing in height on a side away from the first end portion. The condensate which adheres to the first end portion can thus flow toward the side away from the second end portion and the condensate which adheres to the second end portion can flow toward the side away from the first end portion. Therefore, the condensate is less likely to be gathered at the top end of the tip end portion. Therefore, connection between the two electrodes by the condensate gathered at the top end of the tip end portion and resulting conduction between the two electrodes can further be suppressed.

In the hot water apparatus, the groove portion includes an inclined wall portion provided at the top end of the tip end portion. The inclined wall portion has a down grade decreasing in height two-dimensionally from the top end toward the bottom end of the tip end portion. Thus, by causing the condensate to flow along the down grade of the inclined wall portion decreasing in height two-dimensionally, the condensate can be more likely to flow through the groove portion.

In the hot water apparatus, the inclined wall portion is provided to surround the electrode in a circumferential direction of the electrode and to define a tangent of a virtual circle where the electrode is located in a center. Therefore, by setting a virtual circle to ensure insulation, the condensate can be more likely to flow along the inclined wall portion while insulation is ensured.

In the hot water apparatus, the groove portion includes an inclined wall portion provided at the top end of the tip end portion. The inclined wall portion has a down grade decreasing in height in a curved manner from the top end toward the bottom end of the tip end portion. Thus, by causing the condensate to flow along the down grade of the inclined wall portion decreasing in height in a curved manner, the condensate can be more likely to flow through the groove portion.

In the hot water apparatus, the tip end portion includes two cylindrical portions. The two electrodes are inserted in the two respective cylindrical portions in an axial direction of the cylindrical portion. The groove portion is arranged between the two cylindrical portions. The condensate can thus flow through the groove portion arranged between the two cylindrical portions. Insulation of each of the two electrodes can be ensured evenly in a radial direction of the cylindrical portion.

In the hot water apparatus, the tip end portion includes a connection wall arranged between the two cylindrical portions. Each of the two cylindrical portions protrudes from the base end portion relative to the connection wall toward the side away from the wall surface. A top end of the connection wall has a down grade decreasing in height from the base end portion toward the side away from the wall surface. By causing the condensate to flow along the connection wall, the condensate can be more likely to flow through the groove portion.

In the hot water apparatus, the tip end portion protrudes from the base end portion toward the inside of the case. The groove portion is arranged in the inside of the case. Thus, connection between the two electrodes by the condensate gathered at the top end of the tip end portion in the inside of the case and resulting conduction between the two electrodes can be suppressed.

In the hot water apparatus, the tip end portion protrudes from the base end portion toward the outside of the case. The groove portion is arranged outside the case. Thus, connection between the two electrodes by the condensate gathered at the top end of the tip end portion on the outside of the case and resulting conduction between the two electrodes can be suppressed.

In the hot water apparatus, the tip end portion protrudes from the base end portion toward both of the inside and the outside of the case. The groove portion is arranged in both of the inside and the outside of the case. The groove portion arranged in the inside of the case is greater in depth than the groove portion arranged outside the case. Thus, connection between the two electrodes by the condensate gathered at the top end of the tip end portion in both of the inside and the outside of the case and resulting conduction between the two electrodes can be suppressed. The condensate generated in the inside of the case is greater in amount than the condensate generated outside the case. Therefore, the groove portion arranged in the inside of the case is greater in depth than the groove portion arranged outside the case, so that the condensate generated in the inside of the case can flow in a great amount through the groove portion. Therefore, connection between the two electrodes by the condensate gathered at the top end of the tip end portion in the inside of the case where a greater amount of condensate is generated and resulting conduction between the two electrodes can effectively be suppressed.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a construction of a hot water apparatus in one embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a construction of a sensible heat recovery heat exchanger and a latent heat recovery heat exchanger in one embodiment of the present invention.

FIG. 3 is a perspective view schematically showing a construction of the sensible heat recovery heat exchanger in one embodiment of the present invention.

FIG. 4 is a cross-sectional view schematically showing the construction of the sensible heat recovery heat exchanger in one embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view showing a portion around an ignition plug in FIG. 4 as being enlarged.

FIG. 6 is a view in a direction shown with an arrow A in FIG. 5.

FIG. 7 is a perspective view showing the construction viewed from a side of the ignition plug arranged outside the case in one embodiment of the present invention.

FIG. 8 is a perspective view showing the construction viewed from the side of the ignition plug arranged in the inside of the case in one embodiment of the present invention.

FIG. 9 is an enlarged front view of a portion around the ignition plug in FIG. 2 as being enlarged.

FIG. 10 is a front view showing the construction viewed from the side of the ignition plug arranged in the inside of the case in one embodiment of the present invention.

FIG. 11 is a perspective view showing a state of adhesion of condensate to the ignition plug in a comparative example.

FIG. 12 is a perspective view showing a state of adhesion of condensate to the ignition plug in one embodiment of the present invention.

FIG. 13 is a front view showing a first modification of the ignition plug.

FIG. 14 is a front view showing a second modification of the ignition plug.

FIG. 15 is a top view showing a third modification of the ignition plug.

FIG. 16 is a perspective view showing a construction viewed from a side of the third modification of the ignition plug arranged outside the case.

FIG. 17 is a perspective view showing the construction viewed from the side of the third modification of the ignition plug arranged in the inside of the case.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings.

A construction of a hot water apparatus in one embodiment of the present invention will initially be described with reference to FIG. 1.

As shown in FIG. 1, a hot water apparatus 100 in the present embodiment mainly includes a sensible heat recovery heat exchanger (primary heat exchanger) 10, an ignition plug 14, a latent heat recovery heat exchanger (secondary heat exchanger) 20, a burner 30, a chamber 31, a fan assembly 32, a duct 33, a venturi 34, an orifice 35, a gas valve 36, a pipe 40, a bypass pipe 41, a three-way valve 42, a liquid to liquid heat exchanger 43, a hydronic pipe 44, and a housing 50. All of components except for housing 50 among the components above are arranged in housing 50.

Gas valve 36, orifice 35, and venturi 34 are connected to the pipe in this order. A fuel gas can be supplied from the outside of housing 50 to this pipe. The fuel gas supplied to this pipe flows to venturi 34 through gas valve 36 and orifice 35.

Gas valve 36 is configured to control a flow rate of the fuel gas. Venturi 34 is configured to increase a flow velocity of a mixture gas by reducing the flow of the mixture gas of the fuel gas and air. Venturi 34 is constructed to take in air from the outside of housing 50. Venturi 34 is constructed to mix air taken in from the outside of housing 50 and the fuel gas supplied through the pipe.

Venturi 34 is connected to fan assembly 32 through the pipe. The mixture gas mixed in venturi 34 is sent through this pipe to fan assembly 32. Fan assembly 32 is configured to send the mixture gas to burner 30. Fan assembly 32 mainly includes a fan case, an impeller arranged in the fan case, and a drive source (such as a motor) for rotating the impeller.

Fan assembly 32 is connected to chamber 31 and chamber 31 is connected to burner 30. The mixture gas sent from fan assembly 32 is sent through chamber 31 to burner 30.

Burner 30 is configured to generate a combustion gas for heating by burning the mixture gas. Burner 30 is an inverse combustion type apparatus which supplies a combustion gas downward. The mixture gas issued from burner 30 is ignited by ignition plug 14 and becomes the combustion gas. Ignition plug 14 is attached to sensible heat recovery heat exchanger 10 as will be described later.

Burner 30, sensible heat recovery heat exchanger 10, and latent heat recovery heat exchanger 20 are connected such that the combustion gas sequentially passes through sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20. Each of sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20 is provided below burner 30. Specifically, sensible heat recovery heat exchanger 10 is attached under burner 30 and latent heat recovery heat exchanger 20 is attached under sensible heat recovery heat exchanger 10.

Duct 33 is connected to latent heat recovery heat exchanger 20 and duct 33 extends to the outside of housing 50. The combustion gas which has passed through latent heat recovery heat exchanger 20 is thus emitted to the outside of housing 50 through duct 33.

Each of sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20 is configured to heat water and/or hot water with the combustion gas. Specifically, each of sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20 is configured to heat water and/or hot water by exchanging heat between the combustion gas supplied from burner 30 and water and/or hot water.

Sensible heat recovery heat exchanger 10 is configured to recover sensible heat of the combustion gas generated by burner 30. Latent heat recovery heat exchanger 20 is configured to recover latent heat of the combustion gas. For example, a plate type heat exchanger is employed as latent heat recovery heat exchanger 20.

When a temperature of incoming water and/or hot water is low in sensible heat recovery heat exchanger 10 or when an amount of heating by burner 30 is small, water vapor in the combustion gas is condensed in sensible heat recovery heat exchanger 10 and condensed water (drainage water) is generated. Drainage water is generated also in latent heat recovery heat exchanger 20. Drainage water is drained to the outside of housing 50 through a part of duct 33. When a temperature of air is high on the outside of sensible heat recovery heat exchanger 10 and a temperature of incoming water and/or hot water is low in sensible heat recovery heat exchanger 10, condensate which is condensate of water vapor in air is generated outside sensible heat recovery heat exchanger 10. Condensate (drainage water) which is condensate of water vapor in the combustion gas is generated in the inside of sensible heat recovery heat exchanger 10 and condensate which is condensate of water vapor in air is generated outside sensible heat recovery heat exchanger 10. Condensate is likely in a portion of a heat absorption pipe which will be described later in both of the inside and the outside of sensible heat recovery heat exchanger 10.

A heat absorption pipe of sensible heat recovery heat exchanger 10 and a heat absorption pipe of latent heat recovery heat exchanger 20 are connected to each other through pipe 40. A part of pipe 40 on a water entry side relative to latent heat recovery heat exchanger 20 and a part of pipe 40 on a hot water exit side relative to sensible heat recovery heat exchanger 10 are bypassed by bypass pipe 41.

The part of pipe 40 on the hot water exit side relative to sensible heat recovery heat exchanger 10 and bypass pipe 41 are connected to each other by three-way valve 42. Three-way valve 42 is constructed to be able to switch between a flow path from sensible heat recovery heat exchanger 10 to a hot water outlet of pipe 40 and a flow path from sensible heat recovery heat exchanger 10 to bypass pipe 41.

Liquid to liquid heat exchanger 43 is connected to bypass pipe 41. Hydronic pipe 44 connected to a hydronic terminal is inserted in liquid to liquid heat exchanger 43. Liquid to liquid heat exchanger 43 is constructed such that warm water warmed as a result of passage through sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20 flows in liquid to liquid heat exchanger 43. As warm water which flows in liquid to liquid heat exchanger 43 flows outside hydronic pipe 44, heat can be exchanged between warm water which flows in liquid to liquid heat exchanger 43 and warm water which flows in hydronic pipe 44.

Water supplied to hot water apparatus 100 becomes hot as a result of heat exchange with the combustion gas in sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20. Hot water can thus be supplied by hot water apparatus 100.

Warm water which returns from the hydronic terminal passes through hydronic pipe 44 to be warmed as a result of heat exchange with warm water warmed by sensible heat recovery heat exchanger 10 and latent heat recovery heat exchanger 20 in liquid to liquid heat exchanger 43 and thereafter it is supplied again to the hydronic terminal. Warm water can thus be supplied to the hydronic terminal by hot water apparatus 100.

A construction of sensible heat recovery heat exchanger (heat exchanger) 10 included in hot water apparatus 100 will now be described with reference to FIGS. 2 to 4.

As shown in FIG. 2, sensible heat recovery heat exchanger 10 in the present embodiment mainly includes a case 11, a header 12, a heat absorption pipe (heat transfer tube: FIGS. 3 and 4) 13, a fin 16 (FIG. 4), a pressing member 17, and a fixing member 18.

Case 11 includes a first sidewall 11 a, a second sidewall 11 b, a third sidewall 11 c, and a fourth sidewall 11 d. First sidewall 11 a to fourth sidewall 11 d are connected to form a quadrangular frame.

First sidewall 11 a and third sidewall 11 c face each other. Second sidewall 11 b and fourth sidewall 11 d face each other. Each of first sidewall 11 a to fourth sidewall 11 d has a wall surface serving as a partition between the inside and the outside of case 11.

Case 11 in a form of the frame opens upward and downward. The combustion gas can thus be supplied to the inside of case 11 through the upper opening of case 11. The combustion gas can be exhausted to the outside of case 11 through the lower opening of case 11.

Header 12 is provided on an outer surface of first sidewall 11 a. A joint 13 a on the water entry side and a joint 13 b on the hot water exit side are attached to header 12 provided on the outer surface of first sidewall 11 a. A not-shown header is provided also on an outer surface of third sidewall 11 c.

As shown in FIG. 3, header 12 provided on the outer surface of first sidewall 11 a and header 12 provided on the outer surface of third sidewall 11 c are connected to each other through a plurality of heat absorption pipes 13. The plurality of heat absorption pipes 13 include heat absorption pipes 13 located in the inside of case 11 and heat absorption pipes 13 located outside case 11.

A flow of water and/or hot water which flows through headers 12 and heat absorption pipes 13 is, for example, as follows.

Water and/or hot water which comes in from joint 13 a on the water entry side enters heat absorption pipe 13 located in the inside of case 11 through header 12 provided on a side closest to one end of the outer surface of first sidewall 11 a. Water and/or hot water which enters heat absorption pipe 13 reaches not-shown header 12 provided on the outer surface of third sidewall 11 c. Water and/or hot water which reaches header 12 provided on the outer surface of third sidewall 11 c reaches header 12 provided on the outer surface of first sidewall 11 a through another heat absorption pipe 13 connected to header 12.

Thus, water and/or hot water moves from a side of first sidewall 11 a toward third sidewall 11 c and thereafter turns back from the side of third sidewall 11 c toward first sidewall 11 a. Thereafter, water and/or hot water flows as repeating turning back toward third sidewall 11 c and turning back toward first sidewall 11 a.

As shown in FIG. 2, water and/or hot water which reaches header 12 provided on a side closest to the other end of the outer surface of first sidewall 11 a reaches header 12 provided on the outer surface of third sidewall 11 c through heat absorption pipe 13 provided on an outer surface of second sidewall 11 b.

As shown in FIG. 3, water and/or hot water which reaches header 12 provided on the outer surface of third sidewall 11 c reaches header 12 provided on the outer surface of first sidewall 11 a through heat absorption pipe 13 provided on an outer surface of fourth sidewall 11 d and finally exits from joint 13 b on the side of hot water.

As shown in FIG. 4, a plurality of fins 16 are connected to outer circumferential surfaces of heat absorption pipes 13 located in the inside of case 11. FIG. 3 does not show fins for the sake of brevity of description.

Second sidewall 11 b is provided with a recess 11 ba recessed from the outside toward the inside of case 11. At least a part of heat absorption pipe 13 located outside case 11 and on the side of second sidewall 11 b is fitted into recess 11 ba.

Fourth sidewall 11 d is provided with a recess 11 da recessed from the outside toward the inside of case 11. At least a part of heat absorption pipe 13 located outside case 11 and on the side of fourth sidewall 11 d is fitted into recess 11 da.

As shown in FIGS. 3 and 4, ignition plug 14 is attached to the wall surface of case 11 so as to be located from the inside to the outside of case 11. Ignition plug 14 is attached to second sidewall 11 b, for example, to pass through second sidewall 11 b.

Ignition plug 14 is arranged directly under heat absorption pipe 13 located closest to burner 30 (uppermost heat absorption pipe 13) among the plurality of heat absorption pipes 13 located outside case 11 and on the side of second sidewall 11 b.

Ignition plug 14 includes at least two electrodes. In other words, ignition plug 14 includes two or more electrodes. In the present embodiment, ignition plug 14 includes, for example, a pair of ignition plug electrodes 14 a and a flame rod electrode 14 b. The pair of ignition plug electrodes 14 a is configured to generate flames of a mixture gas injected from burner 30 by emitting sparks. Flame rod electrode 14 b is configured to detect flames by sensing a direct current which flows from flame rod electrode 14 b to flames by applying an alternating current voltage across flames generated by burner 30 and making use of conductivity and a rectifying function owing to ionization of the flames. One ignition plug electrode 14 a and one flame rod electrode 14 b may be provided. Only a pair of ignition plug electrodes 14 a may be provided, without providing flame rod electrode 14 b.

Ignition plug 14 includes an insulator portion 14 c. Insulator portion 14 c is attached to the wall surface of case 11. In the present embodiment, each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b passes through insulator portion 14 c and held by insulator portion 14 c. Each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b extends from the inside to the outside of case 11 through insulator portion 14 c. The pair of ignition plug electrodes 14 a and flame rod electrode 14 b are arranged at a distance from one another in a lateral direction (a direction orthogonal to a vertical direction). The pair of ignition plug electrodes 14 a and flame rod electrode 14 b are arranged, for example, as being aligned in the lateral direction. Each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b is made of a conductive material such as a metal. Insulator portion 14 c is made of an insulating material such as ceramics.

Insulator portion 14 c has a main body portion 14 ca and a flange portion 14 cb. Main body portion 14 ca holds each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b. Flange portion 14 cb extends outward from an outer circumferential surface of main body portion 14 ca. Insulator portion 14 c is constructed in an oblong shape in a front view.

A through hole (not shown) is provided in second sidewall 11 b. Insulator portion 14 c is inserted in the through hole in second sidewall 11 b. In the inserted state, a tip end of each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b is located in the inside of case 11.

In the inserted state, main body portion 14 ca in insulator portion 14 c has one end portion located in the inside of case 11. Main body portion 14 ca has the other end portion located outside case 11.

In the inserted state, flange portion 14 cb is located outside case 11. Flange portion 14 cb has a dimension greater than a dimension of opening of the through hole in second sidewall 11 b.

As shown in FIGS. 2 and 6, pressing member 17 presses flange portion 14 cb from a side opposite to second sidewall 11 b. Pressing member 17 is fixed to second sidewall 11 b by fixing member 18 while it presses flange portion 14 cb.

Fixing member 18 may be a screwing member such as a screw or a bolt or a pin. Fixing member 18 passes through second sidewall 11 b and fixing member 18 has a tip end located in the inside of case 11.

Pressing member 17 is fixed to second sidewall 11 b from the outside of case 11 by fixing member 18. Ignition plug 14 can thus securely be fixed to case 11. As shown in FIG. 6, a gasket 19 (FIG. 6) lies between pressing member 17 and second sidewall 11 b. Gasket 19 prevents the combustion gas from leaking from the inside to the outside of case 11. Fixing member 18 may pass through gasket 19.

Ignition plug 14 will now be described in further detail with reference to FIGS. 5 to 10.

As shown in FIGS. 5 and 6, main body portion 14 ca of insulator portion 14 c of ignition plug 14 has a base end portion 14 ca 1 and a tip end portion 14 ca 2. Base end portion 14 ca 1 is attached to the wall surface of case 11. Specifically, base end portion 14 ca 1 is attached to the wall surface of second sidewall 11 b. In the inserted state, base end portion 14 ca 1 is inserted in the through hole in second sidewall 11 b.

Tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward a side opposite to the wall surface of case 11. In the present embodiment, tip end portion 14 ca 2 protrudes toward both of the inside and the outside of case 11. Main body portion 14 ca of insulator portion 14 c has a first tip end portion 14 ca 2 which protrudes toward the inside of case 11 and a second tip end portion 14 ca 2 which protrudes toward the outside of case 11. Tip end portion 14 ca 2 should only protrude toward at least any of the inside and the outside of case 11.

As shown in FIGS. 6 to 8, in the present embodiment, each of first tip end portion 14 ca 2 which protrudes toward the inside of case 11 and second tip end portion 14 ca 2 which protrudes toward the outside of case 11 has a tip end surface TS and a groove portion DP. Tip end surface TS is arranged opposite to base end portion 14 ca 1. Groove portion DP is constructed to be recessed from tip end surface TS toward base end portion 14 ca 1. Groove portions DP are arranged among the pair of ignition plug electrodes 14 a and flame rod electrode 14 b. Portions of the insulator portions where the pair of ignition plug electrodes 14 a and flame rod electrode 14 b are held are arranged at a distance from one another in the lateral direction in tip end surface TS.

As shown in FIGS. 9 and 10, groove portion DP is provided across top and bottom ends TE and BE of tip end portion 14 ca 2. Groove portion DP is provided to pass through from top end TE to bottom end BE of tip end portion 14 ca 2.

Groove portion DP has a lateral width decreasing from top end TE toward bottom end BE of tip end portion 14 ca 2. Groove portion DP should only include a portion decreasing in width from top end TE toward bottom end BE and bottom end BE does not have to be smallest in width. In the present embodiment, groove portion DP has a width decreasing from top end TE of tip end portion 14 ca 2 to a portion between top end TE and bottom end BE. Groove portion DP may decrease in width continuously from top end TE to bottom end BE of tip end portion 14 ca 2.

Groove portion DP has an inclined wall portion DPa and a linear wall portion DPb. Inclined wall portion DPa is provided at top end TE of tip end portion 14 ca 2. Inclined wall portion DPa has a down grade decreasing in height two-dimensionally from top end TE toward bottom end BE of tip end portion 14 ca 2. Inclined wall portion DPa is constructed to surround the entire circumference of groove portion DP in a plan view. Inclined wall portion DPa is located above the pair of ignition plug electrodes 14 a and flame rod electrode 14 b.

Linear wall portion DPb is connected to a bottom end of inclined wall portion DPa. Linear wall portion DPb is constructed to linearly extend in the vertical direction. Linear wall portion DPb has a constant lateral width. Groove portion DP does not have to include linear wall portion DPb.

Tip end portion 14 ca 2 has one end portion (a first end portion) EP1 arranged on one side (a first side) of groove portion DP and the other end portion (a second end portion) EP2 arranged on the other side (a second side) of groove portion DP in the lateral direction. One end portion EP1 has a down grade decreasing in height on a side opposite to the other end portion EP2. One end portion EP1 has a down grade decreasing in height on a side away from the other end portion EP2. The other end portion EP2 has a down grade decreasing in height on a side opposite to one end portion EP1. The other end portion EP2 has a down grade decreasing in height on a side away from one end portion EP1. Top end TE of each of one end portion EP1 and the other end portion EP2 is in such a curved shape as decreasing in height outward in the lateral direction. Specifically, top end TE of each of one end portion EP1 and the other end portion EP2 is in a shape of an arc.

As shown in FIG. 6, groove portion DP has a width increasing from base end portion 14 ca 1 toward tip end surface TS. In a plan view, groove portion DP opens on a side of tip end surface TS and a distance between opposing walls defining groove portion DP increases toward tip end surface TS.

As shown in FIGS. 3 and 6, in the present embodiment, tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward the inside of case 11. Groove portion DP is arranged in the inside of case 11. In addition, as shown in FIGS. 2 and 6, tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward the outside of case 11. Groove portion DP is arranged outside case 11.

As shown in FIGS. 2, 3, and 6, in the present embodiment, tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward both of the inside and the outside of case 11. Groove portion DP is arranged in both of the inside and the outside of case 11. Groove portion DP arranged in the inside of case 11 is greater in depth than groove portion DP arranged outside case 11.

Functions and effects of the present embodiment will now be described in comparison with a comparative example.

As shown in FIG. 11, in a comparative example, groove portion DP has a constant width from top end TE to bottom end BE of tip end portion 14 ca 2. Groove portion DP does not decrease in width from top end TE toward bottom end BE of tip end portion 14 ca 2. Therefore, condensate which adheres to top end TE of tip end portion 14 ca 2 is less likely to flow through groove portion DP. Therefore, condensate gathered at top end TE of tip end portion 14 ca 2 connects two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b and consequently the two electrodes are likely to conduct to each other.

In contrast, according to the present embodiment, as shown in FIG. 12, groove portion DP is recessed from tip end surface TS toward base end portion 14 ca 1, arranged among the pair of ignition plug electrodes 14 a and flame rod electrode 14 b, and provided across top and bottom ends TE and BE of tip end portion 14 ca 2. Groove portion DP has a lateral width decreasing from top end TE toward bottom end BE of tip end portion 14 ca 2. Condensate which is generated on the wall surface of second sidewall 11 b and drops and adheres to insulator portion 14 c is thus likely to flow through groove portion DP. Therefore, connection between two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b by condensate gathered at top end TE of tip end portion 14 ca 2 and resulting conduction between the two electrodes can be suppressed. Therefore, occurrence of insulation failure between the two electrodes can be suppressed.

As shown in FIG. 6, groove portion DP has a width increasing from base end portion 14 ca 1 toward tip end surface TS. Since condensate is thus less likely to be gathered at top end TE of tip end portion 14 ca 2 from base end portion 14 ca 1 toward tip end surface TS, connection between two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b by condensate gathered at top end TE of tip end portion 14 ca 2 and resulting conduction between the two electrodes can further be suppressed.

As shown in FIG. 12, one end portion EP1 of tip end portion 14 ca 2 has a down grade decreasing in height on the side opposite to the other end portion EP2 and the other end portion EP2 has a down grade decreasing in height on the side opposite to one end portion EP1. Condensate which adheres to one end portion EP1 can thus flow toward the side opposite to the other end portion EP2 and condensate which adheres to the other end portion EP2 can flow toward the side opposite to one end portion EP1. Therefore, condensate is less likely to be gathered at top end TE of tip end portion 14 ca 2. Therefore, connection between two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b by condensate gathered at top end TE of tip end portion 14 ca 2 and resulting conduction between the two electrodes can further be suppressed.

As shown in FIG. 12, inclined wall portion DPa has a down grade decreasing in height two-dimensionally from top end TE toward bottom end BE of tip end portion 14 ca 2. By thus causing condensate to flow along the down grade of inclined wall portion DPa decreasing in height two-dimensionally, the condensate can be more likely to flow through groove portion DP.

As shown in FIGS. 3 and 6, tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward the inside of case 11 and groove portion DP is arranged in the inside of case 11. Thus, connection between two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b by condensate gathered at top end TE of tip end portion 14 ca 2 in the inside of case 11 and resulting conduction between the two electrodes can be suppressed.

As shown in FIGS. 2 and 6, tip end portion 14 ca 2 protrudes from base end portion 14 ca 1 toward the outside of case 11 and groove portion DP is arranged outside case 11. Thus, connection between two electrodes of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b by condensate gathered at top end TE of tip end portion 14 ca 2 on the outside of case 11 and resulting conduction between the two electrodes can be suppressed.

An amount of condensate generated in the inside of case 11 is greater than an amount of condensate generated outside case 11. Therefore, a greater amount of condensate generated in the inside of case 11 can flow through groove portion DP by setting a depth of groove portion DP arranged in the inside of case 11 to be greater than a depth of groove portion DP arranged outside case 11. Therefore, connection between two electrodes by condensate gathered at top end TE of tip end portion 14 ca 2 in the inside of case 11 where a large amount of condensate is generated and resulting conduction between the two electrodes can effectively be suppressed.

Various modifications of ignition plug 14 will now be described with reference to FIGS. 13 to 17. Since various modifications are the same in construction as the present embodiment unless otherwise specified, the same elements have the same reference characters allotted and description thereof will not be repeated.

As shown in FIG. 13, in a first modification of ignition plug 14, inclined wall portion DPa of groove portion DP of ignition plug 14 has a down grade decreasing in height in a curved manner from top end TE toward bottom end BE of tip end portion 14 ca 2. By thus causing condensate to flow along the down grade of inclined wall portion DPa decreasing in height in a curved manner, condensate can be more likely to flow through groove portion DP.

As shown in FIG. 14, in a second modification of ignition plug 14, inclined wall portion DPa of groove portion DP of ignition plug 14 has a down grade decreasing in height two-dimensionally from top end TE toward bottom end BE of tip end portion 14 ca 2. Inclined wall portion DPa is provided to define a tangent of a virtual circle VC. Virtual circle VC surrounds each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b in the circumferential direction of each electrode such that each electrode is located in the center thereof. Therefore, with virtual circle VC being set to ensure insulation, by causing condensate to flow along the down grade of inclined wall portion DPa decreasing in height two-dimensionally while insulation is ensured, condensate can be more likely to flow through the groove portion.

As shown in FIGS. 15 to 17, in a third modification of ignition plug 14, tip end portion 14 ca 2 is provided with at least two cylindrical portions CP. Specifically, tip end portion 14 ca 2 is provided with three cylindrical portions CP. The pair of ignition plug electrodes 14 a and flame rod electrode 14 b are inserted in three cylindrical portions CP in an axial direction of cylindrical portion CP, respectively. Groove portion DP is arranged between two cylindrical portions CP of three cylindrical portions CP. In the present embodiment, groove portion DP is arranged between two cylindrical portions CP into which the pair of ignition plug electrodes 14 a is inserted and groove portion DP is arranged between cylindrical portion CP into which ignition plug electrode 14 a arranged in the center in the lateral direction is inserted and cylindrical portion CP into which flame rod electrode 14 b is inserted.

In the third modification of ignition plug 14, condensate can flow through groove portion DP arranged between two cylindrical portions CP. Two electrodes inserted in two respective cylindrical portions CP can evenly ensure insulation in a radial direction of cylindrical portion CP.

Tip end portion 14 ca 2 further has a connection wall DPc arranged between two cylindrical portions CP of three cylindrical portions CP. Each of three cylindrical portions CP protrudes from base end portion 14 ca 1 relative to connection wall DPc toward a side opposite to the wall surface of case 11. Each of three cylindrical portions CP protrudes from base end portion 14 ca 1 relative to connection wall DPc toward a side away from the wall surface of case 11. In a direction of extension of each of the pair of ignition plug electrodes 14 a and flame rod electrode 14 b through cylindrical portion CP, connection wall DPc is smaller in thickness dimension than cylindrical portion CP. Top end TE of connection wall DPc has a down grade decreasing in height from base end portion 14 ca 1 toward a side opposite to the wall surface of case 11. Top end TE of connection wall DPc has a down grade decreasing in height from base end portion 14 ca 1 toward a side away from the wall surface of case 11. Thus, by causing condensate to flow along connection wall DPc, condensate can be more likely to flow through groove portion DP.

Though embodiments of the present invention have been described, it should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. 

What is claimed is:
 1. A hot water apparatus comprising: a burner which generates a combustion gas for heating; a heat exchanger which is provided below the burner and heats water and/or hot water with the combustion gas; and an ignition plug which ignites the burner, the heat exchanger including a case having a wall surface serving as a partition between inside and outside, the ignition plug including an insulator portion attached to the wall surface of the case and two electrodes extending from the inside to the outside of the case through respective insulator portions and arranged at a distance from each other in a lateral direction, the insulator portion including a base end portion attached to the wall surface of the case and a tip end portion protruding from the base end portion toward a side opposite to the wall surface, the tip end portion having a tip end surface arranged opposite to the base end portion and a groove portion recessed from the tip end surface toward the base end portion, the groove portion being arranged between the two electrodes and provided across top and bottom ends of the tip end portion, and the groove portion having a lateral width decreasing from the top end toward the bottom end of the tip end portion.
 2. The hot water apparatus according to claim 1, wherein the groove portion has a width increasing from the base end portion toward the tip end surface.
 3. The hot water apparatus according to claim 1, wherein the tip end portion includes a first end portion arranged on a first side of the groove portion and a second end portion arranged on a second side of the groove portion, the first end portion has a down grade decreasing in height on a side away from the second end portion, and the second end portion has a down grade decreasing in height on a side away from the first end portion.
 4. The hot water apparatus according to claim 1, wherein the groove portion includes an inclined wall portion provided at the top end of the tip end portion, and the inclined wall portion has a down grade decreasing in height two-dimensionally from the top end toward the bottom end of the tip end portion.
 5. The hot water apparatus according to claim 4, wherein the inclined wall portion is provided to surround the electrode in a circumferential direction of the electrode and to define a tangent of a virtual circle where the electrode is located in a center.
 6. The hot water apparatus according to claim 1, wherein the groove portion includes an inclined wall portion provided at the top end of the tip end portion, and the inclined wall portion has a down grade decreasing in height in a curved manner from the top end toward the bottom end of the tip end portion.
 7. The hot water apparatus according to claim 1, wherein the tip end portion includes two cylindrical portions, the two electrodes are inserted in the two cylindrical portions, respectively, in an axial direction of the cylindrical portion, and the groove portion is arranged between the two cylindrical portions.
 8. The hot water apparatus according to claim 7, wherein the tip end portion includes a connection wall arranged between the two cylindrical portions, each of the two cylindrical portions protrudes from the base end portion relative to the connection wall toward a side away from the wall surface, and a top end of the connection wall has a down grade decreasing in height from the base end portion toward the side away from the wall surface.
 9. The hot water apparatus according to claim 1, wherein the tip end portion protrudes from the base end portion toward the inside of the case, and the groove portion is arranged in the inside of the case.
 10. The hot water apparatus according to claim 1, wherein the tip end portion protrudes from the base end portion toward the outside of the case, and the groove portion is arranged outside the case.
 11. The hot water apparatus according to claim 1, wherein the tip end portion protrudes from the base end portion toward both of the inside and the outside of the case, the groove portion is arranged in both of the inside and the outside of the case, and the groove portion arranged in the inside of the case is greater in depth than the groove portion arranged outside the case. 